Lattice materials have demonstrated promising potential in engineering applications owing to their exceptional lightweight,high specific strength,and tunable mechanical properties.However,the traditional homogenizatio...Lattice materials have demonstrated promising potential in engineering applications owing to their exceptional lightweight,high specific strength,and tunable mechanical properties.However,the traditional homogenization methods based on the classical elasticity theory struggle to accurately describe the non-classical mechanical behaviors of lattice materials,especially when dealing with complex unit-cell geometries featured by non-symmetric configurations or non-single central node connections.In response to this limitation,this study establishes a generalized homogenization model based on the micropolar theory framework,employing Hill's boundary conditions to precisely predict the equivalent moduli of complex lattice materials.By introducing the independent rotational degree of freedom(DOF)characteristic of the micropolar theory,the proposed model successfully overcomes the limitation of conventional methods in accurately describing the asymmetric deformation and scale effects.We initially calculate the constitutive relations of two-dimensional(2D)cross-shaped multi-node chiral lattices and subsequently extend the method to three-dimensional(3D)lattices,successfully predicting the mechanical properties of both traditional and eccentric body-centered cubic(BCC)lattices.The theoretical model is validated through the finite element numerical verification which shows excellent consistency with the theoretical predictions.A further parametric study investigates the influence of geometric parameters,revealing the underlying size-effect mechanism.This paper provides a reliable theoretical tool for the design and property optimization of complex lattice materials.展开更多
Silicon‐based anode materials have garnered considerable attention in lithium‐ion batteries(LIBs)due to their exceptionally high theoretical capacity and energy density.However,intrinsic challenges,such as significa...Silicon‐based anode materials have garnered considerable attention in lithium‐ion batteries(LIBs)due to their exceptionally high theoretical capacity and energy density.However,intrinsic challenges,such as significant volumetric expansion and the consequent degradation in cycling stability,severely hinder their practical application.As a result,development of silicon anodes that can effectively mitigate volumetric expansions,enhance cycling durability,and improve rate performance has emerged as a critical research focus.However,due to neglect of“size effects”,the modification strategy of silicon‐based electrodes lacks systematic,scientific,and comprehensive guidance.Herein,this review starts from the“size effect”of silicon‐based materials,and reveals in depth the different failure mechanisms of nano‐silicon(Si NPs)and micro‐silicon(μSi).Furthermore,this review provides targeted classification of modification strategies for Si NPs andμSi,and reviews comprehensively,in detail,and in depth the latest research progress on silicon‐based materials.In addition,the review also comprehensively summarizes the cutting‐edge dynamics of matching silicon‐based electrodes with solid electrolytes to construct high‐energy LIBs.It is hoped that this review can provide comprehensive and systematic scientific guidance for modification strategies of silicon‐based electrodes,which is of great significance for promoting the industrialization process of silicon‐based electrodes in high‐energy LIBs.展开更多
As an emerging pollutant,the impact of microplastics’physical properties on key biogeochemical cycles remains unclear.This study investigated the effects and mechanisms of four particle sizes(25,150,200,500μm)of pol...As an emerging pollutant,the impact of microplastics’physical properties on key biogeochemical cycles remains unclear.This study investigated the effects and mechanisms of four particle sizes(25,150,200,500μm)of polyethylene microplastics(PE-MPs)on nitrogen transformation in river systems through a 120-day indoor micro-cultivation experiment.Results indicate that microplastic addition significantly enhanced nitrogen partitioning from the water phase to sediments,leading to reduced total nitrogen and nitrate concentrations in overlying water.Small-sized(25μm)microplastics strongly promoted ammonium nitrogen accumulation in sediments during long-term exposure,while large-sized(500μm)microplastics induced dramatic fluctuations in sediment total nitrogen content,revealing complex adsorption-desorption dynamics.Correlation analysis indicates that sediment ammonium accumulation is significantly positively correlated with iron content.This study reveals that microplastics primarily disrupt nitrogen transformation processes by altering sediment microenvironments and providing microbial attachment sites,ultimately inhibiting nitrification and leading to the accumulation of nitrogen in the sediment as reduced ammonium salts.The study emphasizes that microplastic size is a key physical parameter governing its interference with the nitrogen cycle,providing crucial evidence for scientifically assessing its ecological risks.展开更多
Research on scale effects on flows over weirs has been conducted on a limited basis, primarily focusing on flows upstream of a single-type weir, such as ogee, broad-crested, and sharp-crested (linear and non-linear) w...Research on scale effects on flows over weirs has been conducted on a limited basis, primarily focusing on flows upstream of a single-type weir, such as ogee, broad-crested, and sharp-crested (linear and non-linear) weirs. However, the scale effects downstream of these single-type weirs have not been thoroughly investigated. This study examined the scale effects on flows over a combined weir system consisting of an ogee weir and a sharp-crested weir, both upstream and downstream, utilizing physical modeling at a 1:33.33 scale based on Froude similarity and three-dimensional (3D) computational fluid dynamics (CFD) modeling. The sharp-crested weir in this study was represented by two sluice gates that remain closed and submerged during flood events. The experimental data confirmed that the equivalent discharge coefficients of the combined weir system behaved similarly to those of a sharp-crested weir across various H/P (where H is the total head, and P is the weir height) values. However, scale effects on the discharge rating curve due to surface tension and viscosity could only be minimized when H/P > 0.4, Re > 26 959, and We > 240 (where Re and We are the Reynolds and Weber numbers, respectively), provided that the water depth exceeded 0.042 m above the crest. Additionally, Re greater than 4 × 104 was necessary to minimize scale effects caused by viscosity in flows in the spillway channel and stilling basin (with baffle blocks). The limiting criteria aligned closely with existing literature. This study offers valuable insights for practical applications in hydraulic engineering in the future.展开更多
To elucidate the effects of Cl^(-)and Ca^(2+) on the corrosion and scale formation of 3Cr steel in CO_(2) floodingproduced fluid,corrosion weight loss experiments,and titration experiments were conducted.The resulting...To elucidate the effects of Cl^(-)and Ca^(2+) on the corrosion and scale formation of 3Cr steel in CO_(2) floodingproduced fluid,corrosion weight loss experiments,and titration experiments were conducted.The resulting products were characterized using scanning electron microscopy(SEM),X-ray diffraction(XRD),and X-ray photoelectron spectroscopy(XPS).This study examined the corrosion and scaling behavior of 3Cr steel under the influence of Cl^(-)and Ca^(2+).The results indicate that both Cl^(-)and Ca^(2+)promote the corro sion of 3Cr steel.Notably,Cl^(-)diminishes the promoting effect of Ca^(2+)on corro sion and inhibits scaling,revealing a mutual enhancement between corrosion and scaling.The mechanisms of localized corrosion under varying concentrations of Cl^(-)and Ca^(2+)differ;under-scale corrosion occurs in environments with 5000 mg·L^(-1) Cl^(-),while Cl^(-)induced corrosion is observed in 20000 mg·L^(-1) Cl^(-)environments.This study highlights that under the synergistic effects of Cl^(-),Ca^(2+),and scaling processes,the protective product film dissolves,thereby influencing both corrosion and scaling processes.展开更多
Ethanol steam reforming(ESR)represents a promising route for sustainable hydrogen production,leveraging the high hydrogen content,renewability,and logistical advantages of ethanol.Although Ni-based catalysts are leadi...Ethanol steam reforming(ESR)represents a promising route for sustainable hydrogen production,leveraging the high hydrogen content,renewability,and logistical advantages of ethanol.Although Ni-based catalysts are leading non-noble candidates for ESR,their practical deployment is hindered by compromised H_(2) production efficiency and rapid deactivation.In this work,we combined catalyst synthesis,kinetic analysis,and mechanistic investigation to elucidate the effectsof Ni particle size(3-9 nm)on ESR performance of Ni/CeO_(2) catalysts.These Ni/CeO_(2) catalysts were prepared via a citric acid-assisted coprecipitation method,and systematically characterized using complementary techniques,including high-resolution transmission electron microscopy(HRTEM),in situ X-ray photoelectron spectroscopy(XPS),hydrogen temperature-programmed reduction(H_(2)-TPR),Raman spectroscopy,O_(2)/CO chemisorption,and temperature-programmed surface reaction(TPSR)analyses.Mechanistic study revealed that ethanol dehydrogenation to acetaldehyde is the rate-determining step,defining the intrinsic activity of Ni sites,whereas C-C bond cleavage governs H_(2) selectivity in ESR.At smaller Ni sizes(e.g.,3.1 nm),larger CeO_(2) surface was exposed,which promoted acetaldehyde condensation to acetone,and consequently reduced H_(2) production efficiency.The Ni/CeO_(2) catalyst with~5 nm of Ni particles afforded the highest H_(2) yield(66.3%)and outstanding stability by balancing dehydrogenation activity,H_(2) selectivity,and coking resistance.Conversely,larger Ni particles(>6 nm)facilitated methanation reaction and catalyst deactivation.This work reconciles prior inconsistencies in the Ni size effects on ESR and provides guidance for the design of efficient and durable Ni-based catalysts for H_(2) production.展开更多
Accurate simulation of ice accretion of supercooled large droplet(SLD)is pivotal for the international airworthiness certification of large aircraft.Its complex dynamics behavior and broad particle size distributions ...Accurate simulation of ice accretion of supercooled large droplet(SLD)is pivotal for the international airworthiness certification of large aircraft.Its complex dynamics behavior and broad particle size distributions pose significant challenges to reliable CFD predictions.A numerical model of multi-particle SLD coupling breaking,bouncing and splashing behaviors is established to explore the relationship between dynamics behavior and particle size.The results show that the peak value of droplet collection efficiencyβdecreases due to splashing.The bounce phenomenon will make the impact limit S_(m)of the water drops decrease.With the increase of the SLD particle size,the water drop bounce point gradually moves toward the trailing edge of the wing.The critical breaking diameter of SLD at an airflow velocity of 50 m/s is approximately 100μm.When the SLD particle size increases,the height of the water droplet shelter zone on the upper edge of the wing gradually decreases,and the velocity in the Y direction decreases first and then increases in the opposite direction,increasing the probability of SLD hitting the wing again.Large particle droplets have a higher effect on the impact limit S_(m)than smaller droplets.Therefore,in the numerical simulation of the SLD operating conditions,it is very important to ensure the proportion of large particle size water droplets.展开更多
The size and shape effect(SSE)of components has become a critical issue for mechanical properties,application reliability,and processing.In this study,the creep rupture life(CRL)of components with different wall thick...The size and shape effect(SSE)of components has become a critical issue for mechanical properties,application reliability,and processing.In this study,the creep rupture life(CRL)of components with different wall thicknesses and positions in a combustion chamber casing simulator made of K439B superalloy was investigated.The intrinsic mechanisms of the SSE were explored from the dendrite structure,volume fraction and size of theγ'phase,and element segregation,etc.It is shown that this casting exhibits a strong SSE of creep rupture life,characterized by a significant difference in the CRL values up to 60%with the variation of wall thickness and position in the casing.In terms of casting technology,the influence of SSE on CRL is actually determined by the cooling rate.The SSE on the creep rupture life originates from the dendrite structure(such as the secondary dendrite arm spacing),volume fraction size of theγ'phase in the dendrite trunk,and elements segregation rate.This work may have implications for the design and application of engineering components with large sizes and complex structures.展开更多
In this study,the thermodynamic behaviors of the intrinsic frequency and buckling temperature of rectangular plates of functionally graded materials(FGMs)are explored based on the modified couple stress theory(MCST)an...In this study,the thermodynamic behaviors of the intrinsic frequency and buckling temperature of rectangular plates of functionally graded materials(FGMs)are explored based on the modified couple stress theory(MCST)and the novel dual powerlaw scale distribution theory.The effects of linear,homogeneous,and non-homogeneous temperature fields on the frequency and buckling temperature of FGM microplates are evaluated in detail.The results show that the porosity greatly affects the mechanical properties of FGM plates,reducing their frequency and flexural temperature compared with non-porous plates.Different temperature profiles alter plate frequencies and buckling temperatures.The presence and pattern of scale effect parameters are also shown to be crucial for the mechanical response of FGM plates.The present research aims to provide precise guidelines for the micro-electro-mechanical system(MEMS)fabrication by elucidating the complex interplay between thermal,material,and structural factors that affect the performance of FGM plates in advanced applications.展开更多
Microforming is an effective method to manufacture small metal parts.However,macro forming can not be transferred to microforming directly because of size effects.Flow stress and tribology size effects were studied.Sc...Microforming is an effective method to manufacture small metal parts.However,macro forming can not be transferred to microforming directly because of size effects.Flow stress and tribology size effects were studied.Scaled down copper T2 cylinder compression was carried out with the lubrication of castor oil and without lubrication.The results show that the flow stress decreases with decreasing the initial specimen diameter in both lubrication conditions,and the flow stress decreases by 30 MPa with the initial specimen diameter decreasing from 8 mm to 1 mm.The friction factor increases obviously with decreasing the initial specimen diameter in the case of lubricating with castor oil,and the friction factor increases by 0.11 with the initial specimen diameter decreasing from 8 mm to 1 mm.However,the tribology size effect is not found in the case without lubrication.The reasons of the flow stress and tribology size effects were also discussed.展开更多
The size-dependent band structure of an Si phononic crystal(PnC)slab with an air hole is studied by utilizing the non-classic wave equations of the nonlocal strain gradient theory(NSGT).The three-dimensional(3D)non-cl...The size-dependent band structure of an Si phononic crystal(PnC)slab with an air hole is studied by utilizing the non-classic wave equations of the nonlocal strain gradient theory(NSGT).The three-dimensional(3D)non-classic wave equations for the anisotropic material are derived according to the differential form of the NSGT.Based on the the general form of partial differential equation modules in COMSOL,a method is proposed to solve the non-classic wave equations.The bands of the in-plane modes and mixed modes are identified.The in-plane size effect and thickness effect on the band structure of the PnC slab are compared.It is found that the thickness effect only acts on the mixed modes.The relative width of the band gap is widened by the thickness effect.The effects of the geometric parameters on the thickness effect of the mixed modes are further studied,and a defect is introduced to the PnC supercell to reveal the influence of the size effects with stiffness-softening and stiffness-hardening on the defect modes.This study paves the way for studying and designing PnC slabs at nano-scale.展开更多
Regarding the scale effects on propeller＇s noncavitation hydrodynamics and hydroacoustics, three similar 7bladed highly-skewed propellers in the wake flow are addressed with diameters of 250, 500 and 1 000 mm, respec...Regarding the scale effects on propeller＇s noncavitation hydrodynamics and hydroacoustics, three similar 7bladed highly-skewed propellers in the wake flow are addressed with diameters of 250, 500 and 1 000 mm, respectively. The discrete line-spectrum noise and its standardized spectrum level scaling law, together with the total sound pressure level are analyzed. The non-cavitation noise predictions are completed by both the frequency domain method and the time domain method. As a fluctuated noise source, the time-dependent fluctuated pressure and normal velocity distribution on propeller blades are obtained by the unsteady Reynolds-averaged Navier-Stokes （ URANS ） simulation. Results show that the pressure coefficient distribution of three propellers on the 0.7R section is nearly superposed under the same advance ratio. The periodic thrust fluctuation of three propellers can exactly reflect the tonal components of the axial passing frequency （APF） and the blade passing frequency （BPF）, and the fluctuation enhancement from the small to the middle propeller at the BPF is greater than that from the middle to the big one. By the two noise prediction methods, the increment of the total sound pressure level from the small to the big propeller differs by 2.49 dB. Following the standardized scaling law, the spectrum curves of the middle and big propellers are nearly the same while significantly differing from the small one. The increment of both the line-spectrum level and the total sound pressure increases with the increase in diameter. It is suggested that the model scale of the propeller should be as large as possible in engineering to reduce the prediction error of the empirical scalin~ law and weaken the scale effects.展开更多
To understand the tensile deformation of electro-deposited Cu with nano-scale twins, a numerical study was carried out based on a conventional theory of mechanism-based strain gradient plasticity （CMSG）. The concept...To understand the tensile deformation of electro-deposited Cu with nano-scale twins, a numerical study was carried out based on a conventional theory of mechanism-based strain gradient plasticity （CMSG）. The concept of twin lamella strengthening zone was used in terms of the cohesive interface model to simulate grain-boundary sliding and separation. The model included a number of material parameters, such as grain size, elastic modulus, plastic strain hardening exponent, initial yield stress, as well as twin lamellar distribution, which may contribute to size effects of twin layers in Cu polycrystalline. The results provide information to understand the mechanical behaviors of Cu with nano-scale growth twins.展开更多
The concepts of scale and scale effect in land use were introduced in this study,and the relationship between scale effect and land use was also discussed,which showed the deficiency in present studies and the trend o...The concepts of scale and scale effect in land use were introduced in this study,and the relationship between scale effect and land use was also discussed,which showed the deficiency in present studies and the trend of further studies.展开更多
Micro radial compression tests were carried out on cylindrical specimens of pure copper polycrystals with different grain sizes. Experimental results indicated that phenomena of decreasing forming force, increasing sc...Micro radial compression tests were carried out on cylindrical specimens of pure copper polycrystals with different grain sizes. Experimental results indicated that phenomena of decreasing forming force, increasing scatter of forming force and more irregular surface topography occurred with the increase of grain size. A modified surface model based on dislocations pile-up in surface layer grains, and a flow stress scattering formulation based on standard deviation and grain size distribution were proposed to analyze size effects on forming force in micro compression. The inhomogeneous deformation of surface layer grains was discussed by the main deformation manner of rotation. A good agreement with the experimental results was achieved.展开更多
To investigate the effects of thickness and grain size on mechanical and deformation properties of C5210 phosphor bronze thin sheets, samples with different grain sizes were obtained through annealing heat treatment a...To investigate the effects of thickness and grain size on mechanical and deformation properties of C5210 phosphor bronze thin sheets, samples with different grain sizes were obtained through annealing heat treatment at different temperatures; and then tensile tests of samples with different thicknesses and grain sizes were conducted at room temperature. The results show that yield strength increases with decreasing thickness from 800 to 50 μm, but work hardening exponent and total elongation decrease, and a modified model was proposed to describe the relation between yield strength and thickness; yield strength decreases as the grain size increases, but work hardening exponent shows an increasing trend, total elongation increases to a peak and then decreases. Fracture morphology of tensile specimens was observed by SEM, which indicates that all tensile specimens are ductile fracture. The dimple intensity increases as the specimen thickness increases but reduces with the specimen grain size increasing.展开更多
Spatial scale is a fundamental problem in Geography. Scale effect caused by fractal characteristic of coastline becomes a common focus of coastal zone managers and researchers. In this study, based on DEM and remote s...Spatial scale is a fundamental problem in Geography. Scale effect caused by fractal characteristic of coastline becomes a common focus of coastal zone managers and researchers. In this study, based on DEM and remote sensing images, multi-scale continental coastlines of China were extracted and the fractal characteristic was analyzed. The results are shown as follows. （1） The continental coastline of China fits the fractal model, and the fractal dimension is 1.195. （2） The scale significant differences according to uplift effects with fractal dimensions of coastline have and subsidence segments along the continental coastlines of China. （3） The fractal dimension of coastline has significant spatial heterogeneity according to the coastline types. The fractal dimension of sandy coastline located in Luanhe River plain is 1.109. The dimension of muddy coastline located in northern Jiangsu Plain is 1.059, while that of rocky coastline along southeastern Fujian is 1.293. （4） The length of rocky coastline is affected by scale more than that of muddy and sandy coastline. Since coastline is the conjunction of sea, land and air surface, the study of coastline scale effect is one of the scientific bases for the researches on air-sea-land interaction in multi-scales.展开更多
The influences of I,article size on the mechanical properties of the particulate metal matrix composite;are obviously displayed in the experimental observations. However, the phenomenon can not be predicted directly u...The influences of I,article size on the mechanical properties of the particulate metal matrix composite;are obviously displayed in the experimental observations. However, the phenomenon can not be predicted directly using the conventional elastic-plastic theory. It is because that no length scale parameters are involved in the conventional theory. In the present research, using the strain gradient plasticity theory, a systematic research of the particle size effect in the particulate metal matrix composite is carried out. The roles of many composite factors, such as: the particle size, the Young's modulus of the particle, the particle aspect ratio and volume fraction, as well as the plastic strain hardening exponent of the matrix material, are studied in detail. In order to obtain a general understanding for the composite behavior, two kinds of particle shapes, ellipsoid and cylinder, are considered to check the strength dependence of the smooth or non-smooth particle surface. Finally, the prediction results will be applied to the several experiments about the ceramic particle-reinforced metal-matrix composites. The material length scale parameter is predicted.展开更多
In 2002, six cohorts ofbroodstock bay scallop Argopecten irradians irradians （Ne=1, 2, 10, 30, 50 and control） were randomly chosen from a population of bay scallop to produce offspring. After one year rearing, with...In 2002, six cohorts ofbroodstock bay scallop Argopecten irradians irradians （Ne=1, 2, 10, 30, 50 and control） were randomly chosen from a population of bay scallop to produce offspring. After one year rearing, with the progeny matured, the similar experiment was done to produce the F2 generation. To determine the magnitude of Ne effects, the growth and survival rates in larvae and adult of six F2 groups were compared. Results showed that inbreeding depression existed not only in the Ne=1 group but also in the Ne=2 group. The growth and survival rates of the two groups were significantly lower than those of the other groups （Ne=10, 30, 50, control）, and there were no significant differences among the latter （P〉0.05）. At the same time, the amount of depression in the Ne=1 group was significantly higher than that of the Ne=2 group （P〈0.05）. These results indicated that the low effective population size （Ne）, which increases the possibility of inbreeding, could lead to some harmful effects on the offspring. So it is essential to maintain a high level of Ne in commercial seed production. Fta＇thermore, as the high fecundity of bay scallop might lead to increased inbreeding, selecting broodstock from different growout sites is recommended.展开更多
Considering the lack of theoretical models and ingredients necessary to explain the scaling of the results of propeller cavitation inception and cavitating hydroacoustics from model tests to full scale currently, and ...Considering the lack of theoretical models and ingredients necessary to explain the scaling of the results of propeller cavitation inception and cavitating hydroacoustics from model tests to full scale currently, and the insufficient reflection of the nuclei effects on cavitation in the numerical methods, the cavitating hydrodynamics and cavitation low frequency noise spectrum of three geometrically similar 7-bladed highly skewed propellers with non-uniform inflow are addressed. In this process, a numerical bridge from the multiphase viscous simulation of propeller cavitation hydrodynamics to its hydro-acoustics is built, and the scale effects on performances and the applicability of exist scaling law are analyzed. The effects of non-condensable gas（NCG） on cavitation inception are involved explicitly in the improved Sauer＇s cavitation model, and the cavity volume acceleration related to its characteristic length is used to produce the noise spectrum. Results show that, with the same cavitation number, the cavity extension on propeller blades increases with diameter associated with an earlier shift of the beginning point of thrust decline induced by cavitation, while the three decline slopes of thrust breakdown curves are found to be nearly the same. The power of the scaling law based on local Reynolds number around 0.9R section is determined as 0.11. As for the smallest propeller, the predominant tonal noise is located at blade passing frequency（BPF）, whereas 2BPF for the middle and both 2BPF and 3BPF for the largest, which shows the cavitating line spectrum is fully related to the interaction between non-uniform inflow and fluctuated cavity volume. The predicted spectrum level exceedance from the middle to the large propeller is 6.65 dB at BPF and 5.94 dB at 2BPF. Since it just differs less than 2 dB to the increment obtained by empirical scaling law, it is inferred that the scale effects on them are acceptable with a sufficient model scale, and so do the scaling law. The numerical implementation of cavitating hydrodynamics and hydro-acoustics prediction of propeller in big scale in wake has been completed.展开更多
基金Project supported by the National Natural Science Foundation of China(No.12472077)the supports from Shanghai Gaofeng Project for University Academic Program Development,Fundamental Research Funds for the Central Universities(No.22120240353).
文摘Lattice materials have demonstrated promising potential in engineering applications owing to their exceptional lightweight,high specific strength,and tunable mechanical properties.However,the traditional homogenization methods based on the classical elasticity theory struggle to accurately describe the non-classical mechanical behaviors of lattice materials,especially when dealing with complex unit-cell geometries featured by non-symmetric configurations or non-single central node connections.In response to this limitation,this study establishes a generalized homogenization model based on the micropolar theory framework,employing Hill's boundary conditions to precisely predict the equivalent moduli of complex lattice materials.By introducing the independent rotational degree of freedom(DOF)characteristic of the micropolar theory,the proposed model successfully overcomes the limitation of conventional methods in accurately describing the asymmetric deformation and scale effects.We initially calculate the constitutive relations of two-dimensional(2D)cross-shaped multi-node chiral lattices and subsequently extend the method to three-dimensional(3D)lattices,successfully predicting the mechanical properties of both traditional and eccentric body-centered cubic(BCC)lattices.The theoretical model is validated through the finite element numerical verification which shows excellent consistency with the theoretical predictions.A further parametric study investigates the influence of geometric parameters,revealing the underlying size-effect mechanism.This paper provides a reliable theoretical tool for the design and property optimization of complex lattice materials.
基金supported by The Key R&D Program of Heilongjiang province(2023ZX04A01)The Key Project of Chongqing Technology Innovation and Application Development(2022TIAD‐DEX0024,2023TIAD‐KPX0007)+2 种基金The National Key R&D Program of China(2021YFC2902905)the Beijing Nova Program,the Chongqing Outstanding Youth Fund(2022NSCQ‐JQX3895)the National Natural Science Foundation of China(22109010).
文摘Silicon‐based anode materials have garnered considerable attention in lithium‐ion batteries(LIBs)due to their exceptionally high theoretical capacity and energy density.However,intrinsic challenges,such as significant volumetric expansion and the consequent degradation in cycling stability,severely hinder their practical application.As a result,development of silicon anodes that can effectively mitigate volumetric expansions,enhance cycling durability,and improve rate performance has emerged as a critical research focus.However,due to neglect of“size effects”,the modification strategy of silicon‐based electrodes lacks systematic,scientific,and comprehensive guidance.Herein,this review starts from the“size effect”of silicon‐based materials,and reveals in depth the different failure mechanisms of nano‐silicon(Si NPs)and micro‐silicon(μSi).Furthermore,this review provides targeted classification of modification strategies for Si NPs andμSi,and reviews comprehensively,in detail,and in depth the latest research progress on silicon‐based materials.In addition,the review also comprehensively summarizes the cutting‐edge dynamics of matching silicon‐based electrodes with solid electrolytes to construct high‐energy LIBs.It is hoped that this review can provide comprehensive and systematic scientific guidance for modification strategies of silicon‐based electrodes,which is of great significance for promoting the industrialization process of silicon‐based electrodes in high‐energy LIBs.
文摘As an emerging pollutant,the impact of microplastics’physical properties on key biogeochemical cycles remains unclear.This study investigated the effects and mechanisms of four particle sizes(25,150,200,500μm)of polyethylene microplastics(PE-MPs)on nitrogen transformation in river systems through a 120-day indoor micro-cultivation experiment.Results indicate that microplastic addition significantly enhanced nitrogen partitioning from the water phase to sediments,leading to reduced total nitrogen and nitrate concentrations in overlying water.Small-sized(25μm)microplastics strongly promoted ammonium nitrogen accumulation in sediments during long-term exposure,while large-sized(500μm)microplastics induced dramatic fluctuations in sediment total nitrogen content,revealing complex adsorption-desorption dynamics.Correlation analysis indicates that sediment ammonium accumulation is significantly positively correlated with iron content.This study reveals that microplastics primarily disrupt nitrogen transformation processes by altering sediment microenvironments and providing microbial attachment sites,ultimately inhibiting nitrification and leading to the accumulation of nitrogen in the sediment as reduced ammonium salts.The study emphasizes that microplastic size is a key physical parameter governing its interference with the nitrogen cycle,providing crucial evidence for scientifically assessing its ecological risks.
基金supported by the Ministry of Public Works and Housing of Indonesia and Parahyangan Catholic University(Grant No.II/PD/2023-07/02-SJ).
文摘Research on scale effects on flows over weirs has been conducted on a limited basis, primarily focusing on flows upstream of a single-type weir, such as ogee, broad-crested, and sharp-crested (linear and non-linear) weirs. However, the scale effects downstream of these single-type weirs have not been thoroughly investigated. This study examined the scale effects on flows over a combined weir system consisting of an ogee weir and a sharp-crested weir, both upstream and downstream, utilizing physical modeling at a 1:33.33 scale based on Froude similarity and three-dimensional (3D) computational fluid dynamics (CFD) modeling. The sharp-crested weir in this study was represented by two sluice gates that remain closed and submerged during flood events. The experimental data confirmed that the equivalent discharge coefficients of the combined weir system behaved similarly to those of a sharp-crested weir across various H/P (where H is the total head, and P is the weir height) values. However, scale effects on the discharge rating curve due to surface tension and viscosity could only be minimized when H/P > 0.4, Re > 26 959, and We > 240 (where Re and We are the Reynolds and Weber numbers, respectively), provided that the water depth exceeded 0.042 m above the crest. Additionally, Re greater than 4 × 104 was necessary to minimize scale effects caused by viscosity in flows in the spillway channel and stilling basin (with baffle blocks). The limiting criteria aligned closely with existing literature. This study offers valuable insights for practical applications in hydraulic engineering in the future.
基金the support from the National Natural Science Foundation of China (51774249)the Sichuan Science and Technology Program (21JCQN0066)。
文摘To elucidate the effects of Cl^(-)and Ca^(2+) on the corrosion and scale formation of 3Cr steel in CO_(2) floodingproduced fluid,corrosion weight loss experiments,and titration experiments were conducted.The resulting products were characterized using scanning electron microscopy(SEM),X-ray diffraction(XRD),and X-ray photoelectron spectroscopy(XPS).This study examined the corrosion and scaling behavior of 3Cr steel under the influence of Cl^(-)and Ca^(2+).The results indicate that both Cl^(-)and Ca^(2+)promote the corro sion of 3Cr steel.Notably,Cl^(-)diminishes the promoting effect of Ca^(2+)on corro sion and inhibits scaling,revealing a mutual enhancement between corrosion and scaling.The mechanisms of localized corrosion under varying concentrations of Cl^(-)and Ca^(2+)differ;under-scale corrosion occurs in environments with 5000 mg·L^(-1) Cl^(-),while Cl^(-)induced corrosion is observed in 20000 mg·L^(-1) Cl^(-)environments.This study highlights that under the synergistic effects of Cl^(-),Ca^(2+),and scaling processes,the protective product film dissolves,thereby influencing both corrosion and scaling processes.
基金supported by the National Key Research and Develop-ment Pr0gram of China(Nos.2021YFA1501104 and 2023YFA1506802)the National Natural Science Foundation of China(No.22032001).
文摘Ethanol steam reforming(ESR)represents a promising route for sustainable hydrogen production,leveraging the high hydrogen content,renewability,and logistical advantages of ethanol.Although Ni-based catalysts are leading non-noble candidates for ESR,their practical deployment is hindered by compromised H_(2) production efficiency and rapid deactivation.In this work,we combined catalyst synthesis,kinetic analysis,and mechanistic investigation to elucidate the effectsof Ni particle size(3-9 nm)on ESR performance of Ni/CeO_(2) catalysts.These Ni/CeO_(2) catalysts were prepared via a citric acid-assisted coprecipitation method,and systematically characterized using complementary techniques,including high-resolution transmission electron microscopy(HRTEM),in situ X-ray photoelectron spectroscopy(XPS),hydrogen temperature-programmed reduction(H_(2)-TPR),Raman spectroscopy,O_(2)/CO chemisorption,and temperature-programmed surface reaction(TPSR)analyses.Mechanistic study revealed that ethanol dehydrogenation to acetaldehyde is the rate-determining step,defining the intrinsic activity of Ni sites,whereas C-C bond cleavage governs H_(2) selectivity in ESR.At smaller Ni sizes(e.g.,3.1 nm),larger CeO_(2) surface was exposed,which promoted acetaldehyde condensation to acetone,and consequently reduced H_(2) production efficiency.The Ni/CeO_(2) catalyst with~5 nm of Ni particles afforded the highest H_(2) yield(66.3%)and outstanding stability by balancing dehydrogenation activity,H_(2) selectivity,and coking resistance.Conversely,larger Ni particles(>6 nm)facilitated methanation reaction and catalyst deactivation.This work reconciles prior inconsistencies in the Ni size effects on ESR and provides guidance for the design of efficient and durable Ni-based catalysts for H_(2) production.
基金supported in part by the National Natural Science Foundation of China(No.52276009)。
文摘Accurate simulation of ice accretion of supercooled large droplet(SLD)is pivotal for the international airworthiness certification of large aircraft.Its complex dynamics behavior and broad particle size distributions pose significant challenges to reliable CFD predictions.A numerical model of multi-particle SLD coupling breaking,bouncing and splashing behaviors is established to explore the relationship between dynamics behavior and particle size.The results show that the peak value of droplet collection efficiencyβdecreases due to splashing.The bounce phenomenon will make the impact limit S_(m)of the water drops decrease.With the increase of the SLD particle size,the water drop bounce point gradually moves toward the trailing edge of the wing.The critical breaking diameter of SLD at an airflow velocity of 50 m/s is approximately 100μm.When the SLD particle size increases,the height of the water droplet shelter zone on the upper edge of the wing gradually decreases,and the velocity in the Y direction decreases first and then increases in the opposite direction,increasing the probability of SLD hitting the wing again.Large particle droplets have a higher effect on the impact limit S_(m)than smaller droplets.Therefore,in the numerical simulation of the SLD operating conditions,it is very important to ensure the proportion of large particle size water droplets.
基金financially supported by the National Science and Technology Major Project of China (No.J2019-VI-0004-0117)a Laboratory Fund Project (6142903220101)。
文摘The size and shape effect(SSE)of components has become a critical issue for mechanical properties,application reliability,and processing.In this study,the creep rupture life(CRL)of components with different wall thicknesses and positions in a combustion chamber casing simulator made of K439B superalloy was investigated.The intrinsic mechanisms of the SSE were explored from the dendrite structure,volume fraction and size of theγ'phase,and element segregation,etc.It is shown that this casting exhibits a strong SSE of creep rupture life,characterized by a significant difference in the CRL values up to 60%with the variation of wall thickness and position in the casing.In terms of casting technology,the influence of SSE on CRL is actually determined by the cooling rate.The SSE on the creep rupture life originates from the dendrite structure(such as the secondary dendrite arm spacing),volume fraction size of theγ'phase in the dendrite trunk,and elements segregation rate.This work may have implications for the design and application of engineering components with large sizes and complex structures.
基金Project supported by the National Key Research and Development Program of China(No.2022YFB3207100)Hubei Provincial Strategic Scientist Training Plan(No.2022EJD009)the Fundamental Research Funds for the Central Universities of China(No.2042023kf1041)。
文摘In this study,the thermodynamic behaviors of the intrinsic frequency and buckling temperature of rectangular plates of functionally graded materials(FGMs)are explored based on the modified couple stress theory(MCST)and the novel dual powerlaw scale distribution theory.The effects of linear,homogeneous,and non-homogeneous temperature fields on the frequency and buckling temperature of FGM microplates are evaluated in detail.The results show that the porosity greatly affects the mechanical properties of FGM plates,reducing their frequency and flexural temperature compared with non-porous plates.Different temperature profiles alter plate frequencies and buckling temperatures.The presence and pattern of scale effect parameters are also shown to be crucial for the mechanical response of FGM plates.The present research aims to provide precise guidelines for the micro-electro-mechanical system(MEMS)fabrication by elucidating the complex interplay between thermal,material,and structural factors that affect the performance of FGM plates in advanced applications.
基金Project(2006AA04Z316)supported by the High-tech Research and Development Program of ChinaProject(JC-05-11)supported by the Science Foundation for Distinguished Young Scholars of Heilongjiang Province,ChinaProject(HIT.NSRIF.2008.36)supported by the Natural Scientific Research Innovation Foundation in Harbin Institute of Technology,China。
文摘Microforming is an effective method to manufacture small metal parts.However,macro forming can not be transferred to microforming directly because of size effects.Flow stress and tribology size effects were studied.Scaled down copper T2 cylinder compression was carried out with the lubrication of castor oil and without lubrication.The results show that the flow stress decreases with decreasing the initial specimen diameter in both lubrication conditions,and the flow stress decreases by 30 MPa with the initial specimen diameter decreasing from 8 mm to 1 mm.The friction factor increases obviously with decreasing the initial specimen diameter in the case of lubricating with castor oil,and the friction factor increases by 0.11 with the initial specimen diameter decreasing from 8 mm to 1 mm.However,the tribology size effect is not found in the case without lubrication.The reasons of the flow stress and tribology size effects were also discussed.
基金Project supported by the National Natural Science Foundation of China(No.11872186)the Fundamental Research Funds for the Central Universities of China(No.HUST:2016JCTD114)。
文摘The size-dependent band structure of an Si phononic crystal(PnC)slab with an air hole is studied by utilizing the non-classic wave equations of the nonlocal strain gradient theory(NSGT).The three-dimensional(3D)non-classic wave equations for the anisotropic material are derived according to the differential form of the NSGT.Based on the the general form of partial differential equation modules in COMSOL,a method is proposed to solve the non-classic wave equations.The bands of the in-plane modes and mixed modes are identified.The in-plane size effect and thickness effect on the band structure of the PnC slab are compared.It is found that the thickness effect only acts on the mixed modes.The relative width of the band gap is widened by the thickness effect.The effects of the geometric parameters on the thickness effect of the mixed modes are further studied,and a defect is introduced to the PnC supercell to reveal the influence of the size effects with stiffness-softening and stiffness-hardening on the defect modes.This study paves the way for studying and designing PnC slabs at nano-scale.
基金The National Natural Science Foundation of China(No.51009144)
文摘Regarding the scale effects on propeller＇s noncavitation hydrodynamics and hydroacoustics, three similar 7bladed highly-skewed propellers in the wake flow are addressed with diameters of 250, 500 and 1 000 mm, respectively. The discrete line-spectrum noise and its standardized spectrum level scaling law, together with the total sound pressure level are analyzed. The non-cavitation noise predictions are completed by both the frequency domain method and the time domain method. As a fluctuated noise source, the time-dependent fluctuated pressure and normal velocity distribution on propeller blades are obtained by the unsteady Reynolds-averaged Navier-Stokes （ URANS ） simulation. Results show that the pressure coefficient distribution of three propellers on the 0.7R section is nearly superposed under the same advance ratio. The periodic thrust fluctuation of three propellers can exactly reflect the tonal components of the axial passing frequency （APF） and the blade passing frequency （BPF）, and the fluctuation enhancement from the small to the middle propeller at the BPF is greater than that from the middle to the big one. By the two noise prediction methods, the increment of the total sound pressure level from the small to the big propeller differs by 2.49 dB. Following the standardized scaling law, the spectrum curves of the middle and big propellers are nearly the same while significantly differing from the small one. The increment of both the line-spectrum level and the total sound pressure increases with the increase in diameter. It is suggested that the model scale of the propeller should be as large as possible in engineering to reduce the prediction error of the empirical scalin~ law and weaken the scale effects.
文摘To understand the tensile deformation of electro-deposited Cu with nano-scale twins, a numerical study was carried out based on a conventional theory of mechanism-based strain gradient plasticity （CMSG）. The concept of twin lamella strengthening zone was used in terms of the cohesive interface model to simulate grain-boundary sliding and separation. The model included a number of material parameters, such as grain size, elastic modulus, plastic strain hardening exponent, initial yield stress, as well as twin lamellar distribution, which may contribute to size effects of twin layers in Cu polycrystalline. The results provide information to understand the mechanical behaviors of Cu with nano-scale growth twins.
文摘The concepts of scale and scale effect in land use were introduced in this study,and the relationship between scale effect and land use was also discussed,which showed the deficiency in present studies and the trend of further studies.
基金Project(51375113)supported by the National Natural Science Foundation of China
文摘Micro radial compression tests were carried out on cylindrical specimens of pure copper polycrystals with different grain sizes. Experimental results indicated that phenomena of decreasing forming force, increasing scatter of forming force and more irregular surface topography occurred with the increase of grain size. A modified surface model based on dislocations pile-up in surface layer grains, and a flow stress scattering formulation based on standard deviation and grain size distribution were proposed to analyze size effects on forming force in micro compression. The inhomogeneous deformation of surface layer grains was discussed by the main deformation manner of rotation. A good agreement with the experimental results was achieved.
文摘To investigate the effects of thickness and grain size on mechanical and deformation properties of C5210 phosphor bronze thin sheets, samples with different grain sizes were obtained through annealing heat treatment at different temperatures; and then tensile tests of samples with different thicknesses and grain sizes were conducted at room temperature. The results show that yield strength increases with decreasing thickness from 800 to 50 μm, but work hardening exponent and total elongation decrease, and a modified model was proposed to describe the relation between yield strength and thickness; yield strength decreases as the grain size increases, but work hardening exponent shows an increasing trend, total elongation increases to a peak and then decreases. Fracture morphology of tensile specimens was observed by SEM, which indicates that all tensile specimens are ductile fracture. The dimple intensity increases as the specimen thickness increases but reduces with the specimen grain size increasing.
基金Chinese Academy of Sciences Program, No.KZCX1-YW-12-04 National Natural Science Foundation of China, No.40571129+1 种基金 Natural Science Foundation of Jiangsu Province, No.BK2009627 National High Technology Research and Development Program of China （863 Program）, No.2011BAH23B04
文摘Spatial scale is a fundamental problem in Geography. Scale effect caused by fractal characteristic of coastline becomes a common focus of coastal zone managers and researchers. In this study, based on DEM and remote sensing images, multi-scale continental coastlines of China were extracted and the fractal characteristic was analyzed. The results are shown as follows. （1） The continental coastline of China fits the fractal model, and the fractal dimension is 1.195. （2） The scale significant differences according to uplift effects with fractal dimensions of coastline have and subsidence segments along the continental coastlines of China. （3） The fractal dimension of coastline has significant spatial heterogeneity according to the coastline types. The fractal dimension of sandy coastline located in Luanhe River plain is 1.109. The dimension of muddy coastline located in northern Jiangsu Plain is 1.059, while that of rocky coastline along southeastern Fujian is 1.293. （4） The length of rocky coastline is affected by scale more than that of muddy and sandy coastline. Since coastline is the conjunction of sea, land and air surface, the study of coastline scale effect is one of the scientific bases for the researches on air-sea-land interaction in multi-scales.
基金The project, supported by the National Natural Science Foundation of China (19891180, 19925211) and by the Chinese Academy of Sciences (KJ951-1-201) and "Bai Ren" plan
文摘The influences of I,article size on the mechanical properties of the particulate metal matrix composite;are obviously displayed in the experimental observations. However, the phenomenon can not be predicted directly using the conventional elastic-plastic theory. It is because that no length scale parameters are involved in the conventional theory. In the present research, using the strain gradient plasticity theory, a systematic research of the particle size effect in the particulate metal matrix composite is carried out. The roles of many composite factors, such as: the particle size, the Young's modulus of the particle, the particle aspect ratio and volume fraction, as well as the plastic strain hardening exponent of the matrix material, are studied in detail. In order to obtain a general understanding for the composite behavior, two kinds of particle shapes, ellipsoid and cylinder, are considered to check the strength dependence of the smooth or non-smooth particle surface. Finally, the prediction results will be applied to the several experiments about the ceramic particle-reinforced metal-matrix composites. The material length scale parameter is predicted.
基金This study was supported by the Project of Scientific Innovation of the Chinese Academy of Sciences under contract No.ZKCX2-211the Science and Technology Plans of Shandong Province under contract No.022110107the Science and Technology Plans of Qingdao under contract No.03-1-HH-10.
文摘In 2002, six cohorts ofbroodstock bay scallop Argopecten irradians irradians （Ne=1, 2, 10, 30, 50 and control） were randomly chosen from a population of bay scallop to produce offspring. After one year rearing, with the progeny matured, the similar experiment was done to produce the F2 generation. To determine the magnitude of Ne effects, the growth and survival rates in larvae and adult of six F2 groups were compared. Results showed that inbreeding depression existed not only in the Ne=1 group but also in the Ne=2 group. The growth and survival rates of the two groups were significantly lower than those of the other groups （Ne=10, 30, 50, control）, and there were no significant differences among the latter （P〉0.05）. At the same time, the amount of depression in the Ne=1 group was significantly higher than that of the Ne=2 group （P〈0.05）. These results indicated that the low effective population size （Ne）, which increases the possibility of inbreeding, could lead to some harmful effects on the offspring. So it is essential to maintain a high level of Ne in commercial seed production. Fta＇thermore, as the high fecundity of bay scallop might lead to increased inbreeding, selecting broodstock from different growout sites is recommended.
基金supported by National Natural Science Foundation of China(Grant No.51009144)
文摘Considering the lack of theoretical models and ingredients necessary to explain the scaling of the results of propeller cavitation inception and cavitating hydroacoustics from model tests to full scale currently, and the insufficient reflection of the nuclei effects on cavitation in the numerical methods, the cavitating hydrodynamics and cavitation low frequency noise spectrum of three geometrically similar 7-bladed highly skewed propellers with non-uniform inflow are addressed. In this process, a numerical bridge from the multiphase viscous simulation of propeller cavitation hydrodynamics to its hydro-acoustics is built, and the scale effects on performances and the applicability of exist scaling law are analyzed. The effects of non-condensable gas（NCG） on cavitation inception are involved explicitly in the improved Sauer＇s cavitation model, and the cavity volume acceleration related to its characteristic length is used to produce the noise spectrum. Results show that, with the same cavitation number, the cavity extension on propeller blades increases with diameter associated with an earlier shift of the beginning point of thrust decline induced by cavitation, while the three decline slopes of thrust breakdown curves are found to be nearly the same. The power of the scaling law based on local Reynolds number around 0.9R section is determined as 0.11. As for the smallest propeller, the predominant tonal noise is located at blade passing frequency（BPF）, whereas 2BPF for the middle and both 2BPF and 3BPF for the largest, which shows the cavitating line spectrum is fully related to the interaction between non-uniform inflow and fluctuated cavity volume. The predicted spectrum level exceedance from the middle to the large propeller is 6.65 dB at BPF and 5.94 dB at 2BPF. Since it just differs less than 2 dB to the increment obtained by empirical scaling law, it is inferred that the scale effects on them are acceptable with a sufficient model scale, and so do the scaling law. The numerical implementation of cavitating hydrodynamics and hydro-acoustics prediction of propeller in big scale in wake has been completed.
